Conventionally, various room-temperature-curable polyorganosiloxane compositions which cure at room temperature to produce cured products in a rubber form or the like have been known. Among them, for the use such as a coating material, a potting material, and the like of electric/electronic components, the one of a type that causes a curing reaction by coming into contact with moisture in the air and emits alcohol, acetone, or the like during curing is generally used. The type of room-temperature-curable polyorganosiloxane composition has advantages that it has good workability, is less likely to corrode an electrode and wiring because alcohol or acetone emitted during curing has less corrosiveness with respect to metals, and is excellent also in adhesiveness and so on.
Especially as a conformal coating agent applied to protect electric/electronic components and a surface of a circuit board having these components mounted thereon from a use environment, a coating material made of a low-viscosity room-temperature-curable polyorganosiloxane composition (for example, refer to Patent Reference 1 (JP-A H07-173435) and Patent Reference 2 (JP-A H07-238259)) and a coating material of a type in which a silicone resin is dissolved in a solvent, are used.
However, a cured coating film obtained from the coating material made of the low-viscosity room-temperature-curable polyorganosiloxane composition is fragile and low in hardness and does not have sufficient scratch strength such as scratch resistance. Besides, a coating material of a solvent type containing a silicone resin needs a solvent removal process by heating at the time of curing, and therefore volatilization of a solvent may worsen work environment and cause corrosion and deterioration of the electric/electronic components and the circuit board having these components mounted thereon. Further, when the solvent is tried to be recovered without being released into the air in order to improve the work environment, a large amount of investment is required.